Crystallization and dielectric properties of borate-based ferroelectric PbTiO3 glass-ceramics

Bulk crystallized PbTiO3 (PT) was the major crystalline phase in borate-based glass ceramics with starting composition 39PbO-1BaO-25TiO(2)-9.8Al(2)O(3)-1SiO(2)-24.2B(2)O(3) (mol%). Crystallization of PT starts at >= 520 degrees C and the crystal size and c/a ratio of PT were approximately the same for all samples heat treated between 520 and 700 degrees C. Two transient unidentified phases were induced when crystallized between 520 and 650 degrees C. The first at 520 degrees C followed by a second at 550 degrees C. At > 650 degrees C, PbTi3O7 was present in addition to PbTiO3. The electrical properties of glasses heat treated between 550-700 degrees C were investigated by fixed frequency capacitance measurements and impedance spectroscopy, IS. No permittivity maximum or Curie temperature, T-c, for the PT phase was observed from fixed frequency capacitance measurements for glasses heat treated below 700 degrees C, however IS data analysis using electric modulus (M") spectroscopy revealed the PT phase to have T-c similar to 480 and 440 degrees C for samples heat treated at similar to 550 and 700 degrees C, respectively. The conductivity of the PT phase and the dc conductivity of the glass heat treated at 700 degrees C were significantly higher than those of glasses heat treated at lower temperatures suggesting there is significant compositional differences between the glass heat treated at 700 degrees C compared to those treated at <= 650 degrees C.